The present invention relates to an electric power steering apparatus and an electricity supply system.
In recent years, various types of electric components and electronic control systems for vehicles have been introduced. In-vehicle networks for connecting a plurality of control devices with control lines, such as a controller area network (CAN) have been applied to an increased number of cars. This prevents the wiring from being complicated and allows control devices of various types of actuators to communicate with each other and share information. Also, the CAN permits the control devices to be integrally controlled.
Electric cars, fuel cell cars, and hybrid cars that switch between engine drive and motor drive according to the condition, have, as a vehicle power source, a high-voltage battery that generates high-voltage for actuating the motor for driving the vehicle. Such a high-voltage vehicle has a DC/DC converter. The DC/DC converter uses the voltage of the high-voltage battery as a primary voltage, and steps down the primary voltage to obtain a secondary voltage. An electric power steering apparatus (EPS) installed in a high-voltage vehicle receives driving electricity based on the secondary voltage.
Normally, such a high-voltage vehicle has a host ECU that monitors the state of electricity supply by the high-voltage battery. The host ECU, for example, monitors the voltage supplied of the high-voltage battery. The host ECU inputs a checking signal indicating the state of electricity supply of the high-voltage battery to an EPSECU through the in-vehicle network. Based on the inputted checking signal, the EPSECU, which controls an EPS, supplies driving electricity to an EPS actuator. When the checking signal indicates an abnormality of the high-voltage battery, the EPSECU stops the supply of driving electricity to the EPS actuator. That is, the EPSECU stops power assist control.
However, in a vehicle where various types of actuators are controlled based on mutual communication through an in-vehicle network, a failure in the in-vehicle network can disrupt the input of various types of signals required for various types of control. When the input of the signal is disrupted, the EPSECU cannot determine whether there is an abnormality in a high-voltage battery or the DC/DC converter. In this case, to make the system fail safe, the EPSECU must stop the power assist control even if there is no abnormality in the high-voltage battery and the DC/DC converter.
Conventionally, Japanese Laid-Open Patent Publication No. 2002-186120 discloses a technology for solving these problems. The disclosed technology provides a bypass circuit forming a closed loop to establish redundant control lines connecting the control devices. When an abnormality occurs in any of the control lines forming the in-vehicle network, a bypass line is automatically established. This configuration prevents disruption of signals due to a failure of the in-vehicle network, thereby improving the reliability of control signals.
However, if a complete redundancy of control lines is established by making control lines forming the in-vehicle network redundant as in the above configuration of the bypass lines, the extended total length of the lines increases the manufacturing costs. Also, to avoid the complexity of wiring due to redundant control lines, the wiring layout of control lines needs to be newly designed, which further increases the costs.